Metal gaskets are well known for providing a seal between a cylinder head and a cylinder block of a motor vehicle engine. Typically these gaskets are formed with apertures over the combustion openings of the cylinders, and some gaskets have special sealing elements around the apertures to increase their sealing effectiveness. Such sealing elements may be formed by folding back an annular portion of the gasket about a circular fold line and pressing it against the main body of the gasket to form a stopper seal.
One of the problems associated with stopper seals is an uneven distribution of compression loading around the aperture. It has been discovered that the greatest load on the stopper seal is at or near the bolt-locations, that is, in the areas adjacent to the bolts which typically secure the gasket to the engine block. It is estimated that as much as 65% of the load is concentrated at the bolt-locations.
There are difficulties in sealing the combustion opening of an operating engine which arise from dynamic motion of the engine parts caused by operating conditions such as firing pressures and thermal gradients, for example, as well as parts design and material selection. To overcome these difficulties, it would be highly desirable to provide a stopper seal wherein the load is more evenly distributed and thus the sealing effectiveness is materially increased.